U.S. patent number 10,246,565 [Application Number 14/667,220] was granted by the patent office on 2019-04-02 for rapidly curing adhesives using encapsulated catalyst and focused ultrasound.
This patent grant is currently assigned to The Boeing Company. The grantee listed for this patent is THE BOEING COMPANY. Invention is credited to Alain A Adjorlolo, Thomas I Boundy, Darrin M Hansen, Geoffrey P. McKnight, Andrew P Nowak, Carissa A. Pajel, April R. Rodriguez, Sophia S. Yang.
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United States Patent |
10,246,565 |
Nowak , et al. |
April 2, 2019 |
Rapidly curing adhesives using encapsulated catalyst and focused
ultrasound
Abstract
Methods for making and curing resin-based adhesives are
disclosed using encapsulated amine accelerators activated by
providing ultrasonic energy.
Inventors: |
Nowak; Andrew P (Los Angeles,
CA), McKnight; Geoffrey P. (Los Angeles, CA), Pajel;
Carissa A. (Mill Creek, WA), Yang; Sophia S. (Los
Angeles, CA), Boundy; Thomas I (Agoura Hills, CA),
Rodriguez; April R. (Marina Del Rey, CA), Hansen; Darrin
M (Seattle, WA), Adjorlolo; Alain A (Mukilteo, WA) |
Applicant: |
Name |
City |
State |
Country |
Type |
THE BOEING COMPANY |
Huntington Beach |
CA |
US |
|
|
Assignee: |
The Boeing Company (Chicago,
IL)
|
Family
ID: |
55083267 |
Appl.
No.: |
14/667,220 |
Filed: |
March 24, 2015 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20160280867 A1 |
Sep 29, 2016 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C08F
220/18 (20130101); C09J 163/00 (20130101); B29C
35/0261 (20130101); B05D 3/108 (20130101); C08J
3/28 (20130101); C09J 11/06 (20130101); B05D
3/12 (20130101); C09J 4/00 (20130101); B05D
7/22 (20130101); C08J 3/241 (20130101); C09J
5/00 (20130101); C08J 2363/00 (20130101); B29C
65/08 (20130101); B29C 66/41 (20130101); C09J
2301/412 (20200801); B29L 2031/3082 (20130101); C08J
2363/02 (20130101); B29C 65/483 (20130101); B29C
65/485 (20130101); B29C 66/1122 (20130101); C08G
59/72 (20130101); C09J 2301/416 (20200801); B29C
66/7212 (20130101); C08J 2333/08 (20130101); C08J
2363/04 (20130101); C08J 2363/06 (20130101); B29C
66/7212 (20130101); B29K 2307/04 (20130101) |
Current International
Class: |
C08J
3/28 (20060101); B05D 3/10 (20060101); C09J
163/00 (20060101); C09J 11/06 (20060101); C09J
5/00 (20060101); B29C 65/08 (20060101); C09J
4/00 (20060101); B05D 3/12 (20060101); C08J
3/24 (20060101); B29C 35/02 (20060101); C08F
220/18 (20060101); B05D 7/22 (20060101); B29C
65/48 (20060101); B29C 65/00 (20060101); C08G
59/72 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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|
|
|
|
|
|
0224382 |
|
Jun 1987 |
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EP |
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1411102 |
|
Apr 2004 |
|
EP |
|
2011073191 |
|
Apr 2011 |
|
JP |
|
2004087826 |
|
Oct 2004 |
|
WO |
|
2015002749 |
|
Jan 2015 |
|
WO |
|
Other References
European Search Report for EP Application 15193609.3-1308 dated
Jul. 25, 2016. cited by applicant .
Lensen D. et al. Biodegradable polymeric microcapsules for
selective ultrasound-triggered drug release Soft Matter, 2011, 7,
5417 May 5, 2011. cited by applicant .
Volodkin DM. Matrix Polyelectrolyte Microcapsules: New System for
Macromolecule Encapsulation Langmuir 2004, 20, 3398-3406. Jan. 26,
2004. cited by applicant .
Zhang H. et al. Silica encapsulation of n-octadecane via sol-gel
process: A novel microencapsulated phase-change material with
enhanced thermal conductivity and performance. Journal of Colloid
and Interface Science 2010, 343, 246-255. Nov. 23, 2009. cited by
applicant .
Kolesnikova T.A. et al. Nanocomposite Microcontainers with High
Ultrasound Sensitivity. Adv. Funct. Mater. 2010, 20, 1189-1195.
Jan. 1, 2010. cited by applicant .
Zhao, Du, Lu, Jin, Ge; Potential and problems in
ultrasound-responsive drug delivery systems; International Journal
of Nanomedicine 2013:8 1621-1633; Apr. 19, 2013. cited by applicant
.
Kricheldorf HR. (ed) Handbook of Polymer Synthesis: Part B. Marcel
Dekker, New York. 1992, (Entire Volume For background purposes
only); Dec. 31, 1992. cited by applicant .
Bounds CO, Goetter R, Pojman JA, Vandersall M. Preparation and
Application of Microparticles Prepared via the Primary
Amine-catalyzed Michael Addition of a Trithiol to a Triacrylate.
Journal of Polymer Science Part A: Polymer Chemistry 2012, 50,
409-422; Oct. 14, 2011. cited by applicant .
Petrie EM. Epoxy Adhesive Formulations. McGraw Hill, New York.
2006. (Entire Volume for background purposes only); Dec. 31, 2006.
cited by applicant .
Odian. Principles of Polymerization 3rd Ed. John Wiley and Sons,
New York. 1991 (Entire Volume for background purposes only); Dec.
31, 1991. cited by applicant .
Petrie EM. Handbook of Adhesives and Sealants 2nd Ed. McGraw Hill,
New York. 2007. (Entire Volume for background purposes only); Dec.
31, 2007. cited by applicant.
|
Primary Examiner: Roswell; Jessica M
Attorney, Agent or Firm: Coats & Bennett, PLLC
Claims
What is claimed is:
1. A method for making an on-demand adhesive comprising the steps
of: mixing a resin-based compound with a non-gas-filled
encapsulated catalyst to form an uncured resin-based adhesive,
depositing said uncured resin-based adhesive onto component, said
catalyst encapsulated within a shell, said shell having an average
shell diameter of from about 1 to about 1000 microns, and said
shell having an average shell wall thickness of from about 1 to
about 10% of the shell diameter; directing non-thermal ultrasonic
energy from an ultrasonic energy source through the component, said
ultrasonic energy source emitting ultrasonic energy from a curved
piezoelectric ceramic probe head with the emitted ultrasonic energy
tuned to an ultrasonic energy in the range of from about 0.5 to
about 50 MHz; focusing the non-thermal ultrasonic energy through
the component to a region or point located in the deposited
adhesive; targeting non-thermal ultrasonic energy frequencies
corresponding to a natural resonant frequency of the shell;
rupturing the non-gas-filled encapsulated catalyst; and curing
on-demand the uncured resin-based adhesive.
2. The method of claim 1, wherein the resin-based compound
comprises an epoxy resin-based compound, and the encapsulated
catalyst is a compound selected from the group consisting of: boron
trichloride methyl amine, boron trichloride ethylamine, and
homologues, boron trifluoride methyl amine, boron trifluoride
ethylamine and homologues, boron trifluoride dimethylamine, boron
trifluoride diethylamine, and homologues, boron trifluoride
trimethylamine, boron trifluoride triethylamine, and homologues,
boron trifluoride piperadine, boron trifluoride hexylamine, and
combinations thereof.
3. The method of claim 1, wherein the resin-based compound is an
epoxy resin-based compound selected from the group comprising:
diglycidyl ethers of bisphenol A; diglycidyl ethers of bisphenol F;
N,N,N',N'-tetraglycidyl-4,4'-diaminophenylmethane; p-amino phenol
triglycidyl ether; epoxy phenol novolac resins; epoxy cresol
novolac resins; 1,3,5-triglycidyl isocyanurate;
tris(2,3-epoxypropyl)isocyanurate; glycerol diglycidyl ether;
trimethylolpropane triglycidyl ether, and combinations thereof.
4. The method of claim 3, wherein the step of mixing a resin-based
compound with an encapsulated catalyst to form an uncured
resin-based adhesive further comprising: mixing a thiol-based
curing agent with the epoxy resin-based compound, wherein the
thiol-based curing agent is selected from the group consisting of:
pentaerythritol tetrakis(3-mercaptopropionate); trimethylolpropane
tris(3-mercaptopropionate); 1,3,4-thiadiazole-2,5-dithiol; poly
(ethylene glycol) dithiol; toluene dithiol; benzene dithiol;
1,2-ethanedithiol; tris[2-(3-mercaptopropionyloxy)ethyl]
isocyanurate, other polyols grafted onto isocyanurate backbones and
combinations thereof.
5. The method of claim 4, wherein the encapsulated catalyst is
selected from the group consisting of: N,N dimethyldodecyl amine
and homologues; (1,8-Diazabicycloundec-7-ene); (1,5-diazabicyclo[4,
3, O]non-5-ene), trienthanolamine, piperazine, dimethylimidazol,
1-methylimidazole; nonylphenol; 1-(2-aminoethyl) piperazine, and
combinations thereof.
6. The method of claim 1, wherein the resin-based compound
comprises an acrylate-based compound, wherein the step of mixing a
resin-based compound with an encapsulated catalyst to form an
uncured resin-based adhesive further comprises mixing a thiol-based
curing agent with the resin-based compound and encapsulated
compound, and wherein the thiol-based curing agent is selected from
the group consisting of: pentaerythritol
tertrakis(3-mercaptopropionate); trimethylolpropane
tris(3-mercaptopropionate); 1,3,4-thiadiazole-2,5-dithiol;
poly(ethylene glycol) dithiol; toluene dithiol; benzene dithiol;
1,2-ethanedithiol;
tris[2-(3-mercaptopropionyloxy)ethyl]isocyanurate other polyols
grafted onto isocyanurate backbones, and combinations thereof.
7. The method of claim 6, wherein the encapsulated catalyst is
selected from the group consisting of: aliphatic primary amines,
aliphatic secondary amines, and combinations thereof.
8. The method of claim 6, wherein, the acrylate resin-based
compound is selected from the group comprising: monoacrylates,
diacrylates, triacrylates, tetraacrylates, pentaacrylates and
combinations thereof.
9. A method for applying and curing an on-demand adhesive
comprising the steps of: mixing a resin-based compound with a
non-gas-filled encapsulated catalyst to form an uncured adhesive
material, said catalyst encapsulated within a shell, said shell
having an average shell diameter of from about 1 to about 1000
microns, and said shell having an average shell wall thickness of
from about 1 to about 10% of the shell diameter; applying the
uncured adhesive material onto an interior surface of a first
component having an interior surface and an exterior surface;
positioning an ultrasonic energy source proximate to the exterior
surface of the first component said first component having a
thickness ranging from about 0.1 to about 0.25 inches; directing
non-thermal ultrasonic energy from an ultrasonic energy source
through the first component and focused to a region or point in the
uncured adhesive material applied onto the first component, said
ultrasonic energy source emitting ultrasonic energy from a curved
piezoelectric ceramic probe head with the emitted ultrasonic energy
tuned to an ultrasonic energy in the range of from about 0.5 to
about 50 MHz; focusing the ultrasonic energy through the component
to a region or point located in the deposited adhesive; targeting
ultrasonic energy frequencies corresponding to a natural resonant
frequency of the shell; rupturing the encapsulated catalyst; and
curing on-demand the uncured adhesive material.
10. The method of claim 9, further comprising the step of: prior to
directing ultrasonic energy, applying the uncured adhesive material
onto an interior surface of a second component having an interior
surface and an exterior surface substantially simultaneously with
the step of applying the uncured adhesive material onto an interior
surface of a first component having an interior surface and an
exterior surface, said second component oriented proximate to the
first component, such that a gap exists between the interior
surface of the first component and the interior surface of the
second component.
11. An uncured adhesive material, said uncured adhesive material
comprising in a mixture: a resin-based compound; and a
non-gas-filled encapsulated catalyst; wherein the catalyst is
encapsulated within a shell, said shell having an average shell
diameter of from about 1 to about 1000 microns, and said shell
having an average shell wall thickness of from about 1 to about 10%
of the shell diameter, and wherein the shell ruptures when a
predetermined amount of energy is received by the shell from an
ultrasonic energy source, said ultrasonic energy source configured
to emit emitting ultrasonic energy from a curved piezoelectric
ceramic probe head with the emitted ultrasonic energy tuned to an
ultrasonic energy range of from about 0.5 to about 50 MHz, and
wherein the uncured adhesive material is configured to be cured
on-demand.
12. The adhesive material of claim 11, wherein the resin-based
compound comprises an epoxy resin-based compound, and the
encapsulated catalyst is a compound selected from the group
consisting of: boron trichloride methyl amine, boron trichloride
ethylamine, and homologues, boron trifluoride methyl amine, boron
trifluoride ethylamine and homologues, boron trifluoride
dimethylamine, boron trifluoride diethylamine, and homologues,
boron trifluoride trimethylamine, boron trifluoride triethylamine,
and homologues, boron trifluoride piperadine, boron trifluoride
hexylamine, and combinations thereof.
13. The adhesive material of claim 11, wherein the resin-based
compound comprises an epoxy resin-based compound selected from the
group comprising: diglycidyl ethers of bisphenol A; diglycidyl
ethers of bisphenol F;
N,N,N',N'-tetraglycidyl-4,4'-diaminophenylmethane; p-amino phenol
triglycidyl ether; epoxy phenol novolac resins; epoxy cresol
novolac resins; 1,3,5-triglycidyl isocyanurate;
tris(2,3-epoxypropyl)isocyanurate; glycerol diglycidyl ether;
trimethylolpropane triglycidyl ether, and combinations thereof.
14. The adhesive material of claim 13, further comprising a
thiol-based curing agent mixed with the epoxy resin-based compound,
wherein the thiol-based curing agent is selected from the group
consisting of: pentaerythritol tetrakis(3-mercaptopropionate);
trimethylolpropane tris(3-mercaptopropionate);
1,3,4-thiadiazole-2,5-dithiol; poly(ethylene glycol) dithiol;
toluene dithiol; benzene dithiol; 1,2-ethanedithiol;
tris[2-(3-mercaptopropionyloxy)ethyl] isocyanurate, other polyols
grafted onto isocyanurate backbones and combinations thereof.
15. The adhesive material of claim 14, wherein the encapsulated
catalyst is selected from the group consisting of: N,N
dimethyldodecyl amine and homologues;
(1,8-Diazabicycloundec-7-ene); (1,5-diazabicyclo[4, 3, 0]non-5-ene,
trienthanolamine, piperazine, dimethylimidazol, 1-methylimidazole;
nonylphenol; 1-(2-aminoethyl) piperazine, and combinations
thereof.
16. The adhesive material of claim 11, wherein the resin-based
compound comprises an acrylate resin-based compound, and a
thiol-based curing agent is mixed with the resin-based compound and
encapsulated compound, and wherein the thiol-based curing agent is
selected from the group consisting of: pentaerythritol
tetrakis(3-mercaptopropionate); trimethylolpropane
tris(3-mercaptopropionate); 1,3,4-thiadiazole-2,5-dithiol;
poly(ethylene glycol) dithiol; toluene dithiol; benzene dithiol;
1,2-ethanedithiol;
tris[2-(3-mercaptopropionyloxy)ethyl]isocyanurate, other polyols
grafted onto isocyanurate backbones, and combinations thereof.
17. The adhesive material of claim 16, wherein the encapsulated
catalyst is selected from the group consisting of: aliphatic
primary amines, aliphatic secondary amines, and combinations
thereof.
18. The adhesive material of claim 16, wherein, the acrylate
resin-based compound is selected from the group comprising:
monoacrylates, diacrylates, triacrylates, tetraacrylates,
pentaacrylates and combinations thereof.
19. A component comprising the adhesive material of claim 11.
20. An aircraft comprising the component of claim 19.
21. The method of claim 1, wherein the component comprises at least
one material selected from the group comprising: aluminum and
carbon fiber reinforced plastic.
Description
TECHNOLOGICAL FIELD
The present disclosure relates generally to the field of adhesives.
More specifically, the present disclosure relates to rapidly
curing, on-demand, adhesive systems that possess a non-thermal
trigger, and that are delivered in a form awaiting triggering at a
later time by applying ultrasonic (US) energy.
BACKGROUND
In the manufacture of component parts into a finished product, the
presence of gaps may occur. In some instances such gaps are
undesirable and must be eliminated. Generally, for gaps larger than
about 3 mm, solid shims made out of thermoset plastic or prepreg
are inserted into the gap. However, for gaps occurring that are
smaller than about 3 mm, liquid shims are used. Liquid shims are
typically epoxy-based structural adhesive materials that possess
high compressive strength when the shims harden or "cure" to their
final solid state. For purposes of liquid shims, a high compressive
strength is considered to be greater than from about 8000 psi to
about 14000 psi at 2% offset and at room temperature. It is
understood that shims may be used to account for and fill gaps
anywhere there exists a small dimensional mismatch between adjacent
parts. Additionally, epoxy or acrylate resins may be used to modify
or otherwise "build-up" areas of material surfaces, such as, for
example, composite materials.
Traditional epoxy resins, and other adhesive resin curing systems
are typically governed by understood curing kinetics. In the case
of epoxy resins, the curing of epoxy resin systems is often
governed by the curing kinetics of epoxy resins with
multifunctional amines or thiol reactive groups that are often
combined with a catalyst. Such adhesive systems have limited
manufacturing flexibility due to the relationship between pot life
and cure time. Pot life is understood to be the amount of time
available to make an active epoxy system, and then apply it to the
desired end use before the epoxy system "sets" or "cures" to the
point where it becomes unworkable to apply (because the epoxy has
hardened and will no longer "flow"). Therefore, highly accelerated
epoxy resin adhesive system cure times inevitably lead to shorter,
and often impractical, pot life times. Conversely, an epoxy resin
system having a longer pot life takes a longer time to cure. Longer
adhesive system cure times increase manufacturing time on a
production line, and otherwise lead increased production
inefficiency.
In addition, known epoxy resin- and acrylate resin-based adhesive
systems may require heat to activate a system catalyst and
"trigger" the curing reaction. In many manufacturing systems for
large components, including the aerospace industry, presenting
equipment capable of supplying evenly applied heat to such
components of a certain dimension to trigger adhesive curing is not
possible, not practical, or would significantly increase
manufacturing cost.
An efficient and cost-effective on-demand adhesive system that is
both rapid curing, and that also has a significantly long pot life
would be useful, cost-effective and highly advantageous.
BRIEF SUMMARY
The present disclosure relates methods, systems, kits and
apparatuses for controlling curing of epoxy resin- and acrylate
resin-based adhesives through the use of encapsulated initiators
that can be selectively triggered through the application of
focused ultrasonic energy. For purposes of the present
specification, it is understood that the terms "initiators",
"accelerators" and "catalysts" are used equivalently.
According to one aspect, the present disclosure is directed to a
method for making an adhesive comprising the steps of mixing a
resin-based compound with an encapsulated catalyst to form an
uncured resin-based adhesive, directing ultrasonic energy from an
ultrasonic energy source to the uncured resin-based adhesive,
rupturing the catalyst, and curing the uncured resin-based
adhesive.
According to another aspect, the resin-based compound comprises an
epoxy resin-based compound, and the encapsulated catalyst comprises
a compound selected from the group including boron trichloride
methyl amine, boron trichloride ethylamine, and homologues, boron
trifluoride methyl amine, boron trifluoride ethylamine and
homologues, boron trifluoride dimethylamine, boron trifluoride
diethylamine, and homologues, boron trifluoride trimethylamine,
boron trifluoride triethylamine, and homologues, boron trifluoride
piperadine, boron trifluoride hexylamine, and combinations
thereof.
In another aspect, the resin-based compound is an epoxy resin-based
compound selected from the group including digylcidyl ethers of
bisphenol A; dicgycidyl ethers of bisphenol F;
N,N,N',N'-tetragylcidyl-4,4'-diaminophenylmethane; p-amino phenol
triglycidyl ether; epoxy phenol novolac resins; epoxy cresol
novolac resins; 1,3,5-triglycidyl isocyanurate;
tris(2,3-epoxypropyl)isocyanurate (and isocyanurates); glycerol
diglycidyl ether; trimethylolpropane triglycidyl ether, and
combinations thereof.
In yet another aspect, the step of mixing a resin-based compound
with an encapsulated catalyst to form an uncured resin-based
adhesive further comprises mixing a thiol-based curing agent with
the epoxy resin-based compound, wherein the thiol-based curing
agent is selected from the group including pentaerythritol
tetrakis(3-mercaptopropionate); trimethylolpropane
tris(3-mercaptopropionate); 1,3,4-thiadiazole-2,5-dithiol;
poly(ethylene glycol) dithiol; toluene dithiol; benzene dithiol;
1,2-ethanedithiol (and increasing MW alkane dithiol);
tris[2-(3-mercaptopropionyloxy)ethyl] isocyanurate (and other
polyols grafted onto isocyanurate backbones), and combinations
thereof, with the encapsulated catalyst selected from the group
including N,N dimethyldodecyl amine and homologues; DBU
(1,8-Diazabicycloundec-7-ene); DBN (1,5-diazabicyclo[4, 3,
0]non-5-ene; trienthanolamine; piperazine; dimethylimidazol;
1-methylimidazole; nonylphenol; 1-(2-aminoethyl) piperazine, and
combinations thereof.
According to another aspect, the present disclosure is directed to
a method for making an adhesive comprising the steps of mixing a
resin-based compound, wherein the resin-based compound comprises an
acrylate-based compound, The acrylate resin-based compound is mixed
with an encapsulated catalyst and a thiol-based curing agent,
wherein the thiol-based curing agent is selected from the group
including pentaerythritol tetrakis(3-mercaptopropionate);
trimethylolpropane tris(3-mercaptopropionate);
1,3,4-thiadiazole-2,5-dithiol; poly(ethylene glycol) dithiol;
toluene dithiol; benzene dithiol; 1,2-ethanedithiol (and increasing
MW alkane dithiol); tris[2-(3-mercaptopropionyloxy)ethyl]
isocyanurate (and other polyols grafted onto isocyanurate
backbones), and combinations thereof. The encapsulated catalyst is
selected from the group including aliphatic primary amines,
aliphatic secondary amines, and combinations thereof.
According to a further aspect, the acrylate resin-based compound is
selected from the group including monoacrylates, diacrylates,
triacrylates, tetraacrylates, pentaacrylates and combinations
thereof.
In yet another aspect, the ultrasonic energy source emits
ultrasonic energy in the range of from about 0.5 to about 50
MHz.
According to another aspect, the present disclosure is directed to
a method for applying and curing an adhesive comprising the steps
of, mixing a resin-based compound with an encapsulated catalyst to
form an uncured adhesive material applying the uncured adhesive
material onto an interior surface of a first component having an
interior surface and an exterior surface, positioning an ultrasonic
energy source proximate to the exterior surface of the component,
directing ultrasonic energy from an ultrasonic energy source to the
uncured adhesive material, rupturing the encapsulated first
catalyst, and curing the uncured adhesive material.
In a further aspect, the present disclosure is directed to the
above-recited method and further comprising the step of, prior to
directing ultrasonic energy, applying the uncured adhesive material
onto an interior surface of a second component having an interior
surface and an exterior surface substantially simultaneously with
the step of applying the uncured adhesive material onto an interior
surface of a first component having an interior surface and an
exterior surface, with the second component oriented proximate to
the first component, such that a gap exists between the interior
surface of the first component and the interior surface of the
second component.
According to another aspect, the ultrasonic energy source emits
ultrasonic energy in the range of from about 0.5 to about 50
MHz.
In a further aspect, the present disclosure is directed to an
uncured adhesive material that is curable on-demand. The uncured
adhesive material comprises, in a mixture, a resin-based compound
and an encapsulated catalyst, wherein the catalyst is encapsulated
within a shell, said shell having an average shell diameter of from
about 0.1 to about 1000 microns, and said shell having an average
shell wall thickness of from about 1 to about 10% of the shell
diameter, and wherein the shell ruptures when a predetermined
amount of energy is received by the shell from an ultrasonic energy
source.
In a further aspect, the resin-based compound comprises an epoxy
resin-based compound, and the encapsulated catalyst is a compound
selected from the group including boron trichloride methyl amine,
boron trichloride ethylamine, and homologues, boron trifluoride
methyl amine, boron trifluoride ethylamine and homologues, boron
trifluoride dimethylamine, boron trifluoride diethylamine, and
homologues, boron trifluoride trimethylamine, boron trifluoride
triethylamine, and homologues, boron trifluoride piperadine, boron
trifluoride hexylamine, and combinations thereof.
In yet another aspect, the resin-based compound comprises an epoxy
resin-based compound selected from the group including: digylcidyl
ethers of bisphenol A; dicgycidyl ethers of bisphenol F;
N,N,N',N'-tetragylcidyl-4,4'-diaminophenylmethane; p-amino phenol
triglycidyl ether; epoxy phenol novolac resins; epoxy cresol
novolac resins; 1,3,5-triglycidyl isocyanurate;
tris(2,3-epoxypropyl)isocyanurate (and isocyanurates); glycerol
diglycidyl ether; trimethylolpropane triglycidyl ether, and
combinations thereof.
In another aspect, the present disclosure is directed to an
adhesive material comprising an epoxy resin-based compound, and a
thiol-based curing agent mixed with the epoxy resin-based compound,
wherein the thiol-based curing agent is selected from the group
consisting of: pentaerythritol tetrakis(3-mercaptopropionate);
trimethylolpropane tris(3-mercaptopropionate);
1,3,4-thiadiazole-2,5-dithiol; poly(ethylene glycol) dithiol;
toluene dithiol; benzene dithiol; 1,2-ethanedithiol (and increasing
MW alkane dithiol);
tris[2-(3-mercaptopropionyloxy)ethyl]isocyanurate (and other
polyols grafted onto isocyanurate backbones), and combinations
thereof. In another aspect the encapsulated catalyst is selected
from the group consisting of N,N dimethyldodecyl amine and
homologues; DBU (1,8-Diazabicycloundec-7-ene); DBN
(1,5-diazabicyclo[4, 3, 0]non-5-ene, trienthanolamine, piperazine,
dimethylimidazol, 1-methylimidazole; nonylphenol; 1-(2-aminoethyl)
piperazine; ECA-39; Accelerator, and combinations thereof.
In yet another aspect, the present disclosure is directed to an
uncured adhesive material that is curable on-demand, with the
uncured adhesive material comprising in a mixture, a resin-based
compound and an encapsulated catalyst, wherein the catalyst is
encapsulated within a shell, with the shell having an average shell
diameter of from about 0.1 to about 1000 microns, and the shell
having an average shell wall thickness of from about 1 to about 10%
of the shell diameter, and wherein the shell ruptures when a
predetermined amount of energy is received by the shell from an
ultrasonic energy source. According to one aspect, the resin-based
compound comprises an acrylate resin-based compound, and a
thiol-based curing agent is mixed with the resin-based compound and
encapsulated compound, and the thiol-based curing agent is selected
from the group consisting of: pentaerythritol
tetrakis(3-mercaptopropionate); trimethylolpropane
tris(3-mercaptopropionate); 1,3,4-thiadiazole-2,5-dithiol;
polyethylene glycol) dithiol; toluene dithiol; benzene dithiol;
1,2-ethanedithiol (and increasing MW alkane dithiol);
tris[2-(3-mercaptopropionyloxy)ethyl]isocyanurate (and other
polyols grafted onto isocyanurate backbones), and combinations
thereof. The encapsulated catalyst is selected from the group
including, aliphatic primary amines, aliphatic secondary amines,
and combinations thereof. According to a further aspect, the
acrylate resin-based compound is selected from the group
comprising: monoacrylates, diacrylates, triacrylates,
tetraacrylates, pentaacrylates and combinations thereof, and the
ultrasonic energy source emits ultrasonic energy in the range of
from about 0.5 to about 50 MHz.
According to another aspect, the present disclosure is directed to
a resin-based adhesive material that is curable on-demand, with an
adhesive precursor material comprising an epoxy or acrylate
resin-based compound, a catalyst that is encapsulated wherein the
catalyst is encapsulated within a shell, and the shell having an
average shell diameter of from about 0.1 to about 1000 microns, and
said shell having an average shell wall thickness of from about 1
to about 10% of the shell diameter, and wherein the shell can be
ruptured when a predetermined amount of ultrasonic energy is
received by the shell from an ultrasonic energy source.
According to a further aspect, the present disclosure is directed
to a component comprising a resin-based adhesive material that is
curable on-demand, with the adhesive material comprising an epoxy
resin- or an acrylate resin-based compound, a catalyst that is
encapsulated wherein the catalyst is encapsulated within a shell,
said shell having an average shell diameter of from about 0.1 to
about 1000 microns, and said shell having an average shell wall
thickness of from about 1 to about 10% of the shell diameter, and
wherein the shell can be ruptured when a predetermined amount of
ultrasonic energy is received by the shell from an ultrasonic
energy source.
In a further aspect, the present disclosure is directed to objects
comprising an epoxy or acrylate resin-based adhesive material that
is curable on-demand, with the adhesive material comprising an
epoxy resin-based compound, a catalyst that is encapsulated wherein
the catalyst is encapsulated within a shell, said shell having an
average thickness of from about 0.1 to about 1000, and said shell
having an average shell wall thickness of from about 1 to about 10%
of the shell diameter, and wherein the shell can be ruptured when a
predetermined amount of ultrasonic energy is received by the shell
from an ultrasonic energy source. The contemplated objects include,
but are not limited to vehicles, such as, for example, aircraft,
spacecraft, satellites, rockets, missiles, etc. and therefore
include manned and unmanned aircraft, spacecraft, terrestrial,
non-terrestrial, and even surface and sub-surface water-borne
vehicles, etc.
BRIEF DESCRIPTION OF THE DRAWINGS
Having thus described variations of the disclosure in general
terms, reference will now be made to the accompanying drawings,
which are not necessarily drawn to scale, and wherein:
FIG. 1 is a graph showing the relationship between pot life and
cure time;
FIG. 2 is a block diagram outlining an aspect of the present
disclosure; a method for making an adhesive comprising a
resin-based compound mixed with an encapsulated catalyst and a
thiol curing agent that is exposed to an ultrasonic source to
rupture the encapsulated catalyst and cure the adhesive;
FIG. 3 is a block diagram outlining an aspect of the present
disclosure; a method for making an adhesive comprising an epoxy
resin-based compound mixed with a thiol curing agent and an
encapsulated tertiary amine catalyst that is exposed to an
ultrasonic source to rupture the encapsulated catalyst and cure the
adhesive;
FIG. 4 is a block diagram outlining an aspect of the present
disclosure; a method for making an adhesive comprising an acrylate
resin-based compound mixed with a thiol curing agent and an
encapsulated primary or secondary amine catalyst that is exposed to
an ultrasonic source to rupture the encapsulated catalyst and cure
the adhesive;
FIG. 5 is a block diagram outlining an aspect of the present
disclosure; a method for making an adhesive comprising an epoxy
resin-based compound mixed with an encapsulated tri-fluorinated
amine complex catalyst that is exposed to an ultrasonic source to
rupture the encapsulated catalyst and cure the adhesive;
FIG. 6 is a schematic cross-sectional drawing of an ultrasonic
curing of a liquid shim in place according to an aspect of the
present disclosure;
FIG. 7 is a further schematic cross-sectional drawing of an
ultrasonic curing of a liquid shim in place according to an aspect
of the present disclosure; and
FIG. 8 is drawing of an aircraft comprising component parts
comprising liquid shims made from cured adhesives according to an
aspect of the present disclosure.
DETAILED DESCRIPTION
Aspects of the present disclosure are directed to methods, systems,
kits and compositions for controlling the curing of resin-based
adhesives through the use of encapsulated initiators whose release
may be accomplished when desired by applying focused ultrasonic
energy to the resin system comprising the encapsulated initiators
and/or accelerators. While the general concept of rupturing
partially gas-filled capsules through the use of ultrasonic energy
is known in biomedical fields, especially to facilitate drug
release in vivo, aspects of the present disclosure combine the use
of specially tailored resins and catalysts and/or catalyst pairs
that accelerate cure time, and that can be triggered on-demand via
exposing non-gas-filled encapsulated catalysts to ultrasonic
energy, while also achieving a user-controlled pot life
duration.
In manufacturing, gap-filling materials used to build up surfaces,
or, for example as liquid shims, are understood to have been
limited by their pot life, cure time, compressive strength,
resistance to cyclic fatigue and optimal viscosity (for applying to
vertical surfaces). Longer pot life allows the assembly of larger
components and also aides in the cleanup of unused material.
Excessively long pot life, however, interferes with the rate of
manufacturing, as the shim needs time to fully cure. While
mechanical properties of presently known liquid shims satisfy many
production requirements, a significant limitation of known systems
is the relationship between resin and catalyst creating the liquid
shim materials, especially as they relate to either short pot life
and cure time, or lengthy pot life and cure time. Ideally, a
structural adhesive would have a lengthy pot life combined with a
rapid cure time to achieve the greatest manufacturing efficiency.
Frequently, heat has been used to achieve the desired curing
trigger. However, certain manufacturing environments, for example
the manufacture of aircraft, spacecraft, manned and unmanned
vehicles, satellites, etc., will not permit useful active heating
to be effectively incorporated into the manufacturing and assembly
processes. FIG. 1 shows traditional cure kinetics of a system where
the slow rise in viscosity and hardening of an adhesive essentially
defines the pot life followed by a more rapid curing over a given
time period. In contrast, according to an aspect of the present
disclosure, an ideal cure profile is shown where a cure reaction
can be triggered on-demand. According to aspects of this
disclosure, an ideal cure profile would show complete lack of
viscosity increase (through curing) until the application of a
trigger (e.g. an ultrasonic energy trigger) leading to a rapid
cure. This ideal cure profile has the effect of achieving a
substantially infinite pot life (while the applied adhesive awaits
curing) through the application of ultrasonic energy to rupture the
encapsulated catalyst that is incorporated in the adhesive
system.
According to one aspect, encapsulated primary (1.degree.),
secondary (2.degree.) and tertiary (3.degree.) amine compounds are
selected and used as catalysts in an on-demand and predetermined
regimen to accelerate the curing of epoxy/amine-, epoxy/thiol-
and/or acrylate-based adhesive systems by applying and selectively
targeting an ultrasound energy source through a solid or opaque
boundary to non-thermally trigger curing by rupturing the
encapsulated catalysts.
According to one aspect, the ultrasound source is one that is
capable of transmitting energy through a solid or opaque substrate
to a preselected and encapsulated catalyst target. The ultrasound
energy source is capable of focusing high frequency energy in the
range of about 0.5 to about 50 MHz. The solid substrate through
which the ultrasound energy can be transmitted has a preferred
thickness range of from about 0.1 to about 0.25 inches.
Contemplated resin systems are epoxy-based, or acrylate-based. The
contemplated epoxy resin-based and acrylate-based systems may
comprise multifunctional amine and/or multifunctional thiol
compounds.
According to an aspect of this disclosure, the capsule formation
system may be based on an in situ polymerization technique such as,
for example, water/oil/water ("w/o/w") double emulsion, or complex
coacervate, etc. According to another aspect, an interfacial
polymerization capsule shell comprises, for example,
pentaerythritol tetrakis (3-mercapto proprionate) and
trimethylolpropane triaciylate. The w/o/w double emulsion capsule
shell may comprise polycaprolactone, polyacetic acid. Further the
coacervate capsule may comprise cetyltrimethylammonium bromide
(CTAB), polystyrene sulfonate (PSS) and (poly)allylamine (PAA).
According to one aspect, the capsule or shell may have an average
shell diameter of from about 0.1 to about 1000 microns. According
to a further aspect, the shell has an average shell diameter of
from about 10 to about 100 microns. In yet another aspect, the
shell has an average shell wall thickness of from about 1 to about
10% of the shell diameter. In particular, it is noted that the
encapsulation techniques adapted for use with aspects of the
present disclosure are tailored so as to not introduce gas-filled
regions into the encapsulated catalysts.
The accelerator compounds (tertiary amine catalysts) to be
encapsulated may be chosen from a list including N,N
dimethyldodecyl amine and homologues, DBU
(1,8-Diazabicycloundec-7-ene), DBN (1,5-diazabicyclo[4, 3,
0]non-5-ene, trienthanolamine, piperazine, dimethylimidazol,
1-methylimidazole, nonylphenol, and/or 1-(2-aminoethyl) piperazine.
Further commercially available products that may be useful as
epoxy-based accelerators/catalysts include, ECA-39 (Dow),
Accelerator 399 (Albermarle), etc.
Epoxy resins alone have now been determined to undergo rapid cure
from boron trifluoro amine complexes including, for example,
BF.sub.3:amine complexes, through a cationic ring-opening
polymerization process. Accordingly, further useful epoxy-based
accelerators/catalysts include boron trichloride methyl amine,
boron trichloride ethylamine, and homologues, boron trifluoride
methyl amine, boron trifluoride ethylamine and homologues, boron
trifluoride dimethylamine, boron trifluoride diethylamine, and
homologues, boron trifluoride trimethylamine, boron trifluoride
triethylamine, and homologues, boron trifluoride piperadine, boron
trifluoride hexylamine, and combinations thereof, etc.
According to further aspects, the accelerators to be used with
acrylate resin-based adhesive systems may be chosen from the list
including primary and secondary amines, particularly aliphatic
primary amines and aliphatic secondary amines, and combinations
thereof.
Still further aspects of the present disclosure relate to including
a plurality of differing encapsulated accelerators within an epoxy
resin- and/or acrylate resin-based adhesive system.
To overcome known limitations, the present disclosure describes
compositions and methods designed to use ultrasound energy as a
method to selectively trigger the cure of epoxy or acrylate resin
systems. Ultrasound-based triggers have the benefit of being able
to transmit through solid or opaque media such as, for example,
aluminum or carbon fiber reinforced plastic (CFRP) commonly found
in aerospace manufacturing environments, and that are understood to
not be reliant on a line-of-sight requirement (such as that
required for infrared or UV curable systems).
Manufactured components having a gap between components, and which
would be candidates for employing a liquid shim comprising an epoxy
resin or acrylamide-based resin system according to the present
disclosure may themselves comprise aluminum or CFRP. According to
further aspects, an ultrasound signal source may be oriented or
positioned on, for example, an exterior surface of an aluminum or
CFRP component. The ultrasound source can be focused to a region or
point located within the gap, for a predetermined time and at a
predetermined intensity to insure the desire curing of the epoxy
resin- or acrylamide resin-based compound acting as the liquid
shim. It is further understood that, according to aspects of the
present disclosure, and depending upon the desired curing regimen
selected, the ultrasound source may contact a component exterior
surface, may substantially contact a component exterior surface,
may be located or positioned proximate to a component exterior
surface, etc.
According to aspects of the present disclosure, resin systems are
selectively cured at a predetermined rate by adding an encapsulated
catalyst and providing an ultrasound source that can be selectively
targeted to rupture the encapsulated catalyst. The resin is applied
between dimensional mismatches existing between adjacent
components, or, "gaps" that are ideally less than 3 mm, with the
applied resin acting as a liquid shim. The components have an
exterior surface and an interior surface. The resin is applied to
the gap occurring between the interior surfaces of the adjacent
components. An ultrasound source is disposed to a solid exterior
surface of a component. When the ultrasound source is activated,
the ultrasound energy serves to trigger the curing of the resin by
rupturing the encapsulated resin catalysts in a targeted and
preselected way.
In addition, materials, such as composite materials that may
require the presence of an adhesive material to bond with the
composite and "build up" an area of the composite material will
benefit from aspects of the present disclosure. In such uses, the
epoxy resin- and acrylate resin-based adhesive systems are applied
to one surface of a material, but then can be cured by applying an
ultrasound source that can be focused to a region or point located
within the adhesive layer, for a predetermined time and at a
predetermined intensity to insure the desired curing of the epoxy
resin- or acrylate resin-based adhesive system. It is understood
that if the adhesive is applied, for example, to the interior
surface of a component, the ultrasound source is located proximate
to the exterior surface of the component, or vice versa.
According to aspects of the present disclosure, the contemplated
ultrasound sources are combined with an epoxy- or acrylate
resin-based adhesive system designed to be susceptible to the
application of acoustic enemy, so as to selectively trigger a rapid
curing response in a predetermined and predictable fashion.
Therefore, aspects of the present disclosure contemplate a resin
system capable of being cured at an accelerated rate by adding an
encapsulated catalyst species, as well as the capacity to segregate
the resin from the catalyst until the desired time to trigger the
reaction and curing.
Aspects of the present disclosure therefore provide an "on demand"
ultrasound-triggered system for epoxy resin- and acrylate
resin-based systems. Further aspects contemplate appropriate resin
and encapsulated catalyst pairs capable of being triggered in
response to applied ultrasound energy. Aspects of the present
disclosure, therefore, combine to provide a process for
controllably curing, in situ, epoxy resin- and acrylate resin-based
adhesive systems through the use of an ultrasound trigger. Aspects
of the disclosure further combine to achieve the goal of developing
a curable epoxy resin- and/or acrylate resin-based composition for
use as a liquid shim, with the composition having a virtually
infinite pot life with a preselected user-triggered curing time and
rate.
Further disclosed aspects comprise a resin system capable of being
catalyzed to achieve an accelerated cure, the system comprising at
least one type of encapsulated catalyst dispersed in a resin mix,
and a mechanism for predictably rupturing the encapsulated catalyst
within the resin by a user on-demand. FIG. 2 is a block diagram
showing an aspect of the disclosure. According to system 20,
resin-based compound 22 is mixed with a thiol 24 and an
encapsulated catalyst 26. It is understood that the specific order
of mixing the three components, may occur in any order. That is,
the thiol 24 may be mixed with the resin-based compound 22, or the
resin-based compound 22 and the encapsulated catalyst 26 may be
mixed first, with the thiol 24 then added. The mixture is then
exposed to an ultrasonic source 27, which causes the encapsulated
catalyst 26 to rupture, causing the curing 28 of the adhesive
mixture.
Some representative and contemplated, but non-exclusive, resin
systems are set forth and described below.
In one contemplated system, the adhesive results from combining an
amine catalyst with an epoxy resin and an accelerator. Left
unaccelerated, this system will cure via primary and secondary
amine catalysts with cure times approaching multiple hours to
days.
Tertiary amine catalysts are contemplated as useful encapsulated
accelerators/catalysts in a resin-based adhesive mixture, when the
resin based system is an epoxy resin-based system with the presence
of a thiol curing agent. Useful tertiary amines include
N,N-dimethyldodecyl amine and homologues, DBU
(1,8-Diazabicycloundec-7-ene), DBH
(1,5-Diazabicyclo[4,3,0]non-5-ene), triethanolamine, piperazine,
dimethylimidazole, 1-methylimidazole, nonylphenol, 1-(2-aminoethyl)
piperazine, Epoxy Curing Agent ECA-39 (Dow), Accelerator 399
(Albermarle), and/or various other tertiary amines capable of
accelerating cure when used at between 1-20% by weight with respect
to the resin, and combinations thereof, etc.
In one system, an epoxy resin is combined with a thiol
curing/hardening agent and an encapsulated tertiary amine to
produce a stable, on-demand, rapidly curing epoxy compound. When
uncatalyzed, the resin has an effectively infinite pot life.
However, the release of a tertiary amine catalyst from an
encapsulated state (e.g. in a shell, or capsule, etc.) dispersed
throughout the adhesive resin system mixture provides a
dramatically accelerated cure. Exemplary epoxy resins include
diglycidyl ethers of bisphenol A; dicgycidyl ethers of bisphenol F;
N,N,N',N'-tetragylcidyl-4,4'-diaminophenylmethane; p-amino phenol
triglycidyl ether; epoxy phenol novolac resins; epoxy cresol
novolac resins; 1,3,5-triglycidyl isocyanurate;
tris(2,3-epoxypropyl)isocyanurate (and isocyanurates); glycerol
diglycidyl ether; trimethylolpropane triglycidyl ether, and
combinations thereof, etc. Contemplated tertiary amines useful in
an epoxy resin with thiol system include N,N-dimethyldodecyl amine
and homologues, DBU (1,8-Diazabicycloundec-7-ene), DBH
(1,5-Diazabicyclo[4,3,0]non-5-ene), triethanolamine, piperazine,
dimethylimidazole, 1-methylimidazole, nonylphenol, 1-(2-aminoethyl)
piperazine, Epoxy Curing Agent ECA-39 (Dow), Accelerator 399
(Albermarle), and various other tertiary amines capable of
accelerating cure when used at between 1-20% by weight with respect
to the resin, and combinations thereof, etc. This system is
outlined in the block diagram shown as FIG. 3. According to system
30, epoxy resin-based compound 32 is mixed with a thiol 34 and an
encapsulated tertiary amine catalyst 36. It is understood that the
specific order of mixing the three components, may occur in any
order. That is, the thiol 34 may be mixed with the epoxy
resin-based catalyst 32, or the epoxy resin-based compound 32 and
the encapsulated tertiary amine catalyst 36 may be mixed first,
with the thiol 34 then added. The mixture is then exposed to an
ultrasonic source 37, which causes the encapsulated catalyst 36 to
rupture, causing the curing 38 of the adhesive mixture.
In another contemplated system, an acrylate resin is combined with
a thiol curing/hardening agent and an encapsulated primary or
secondary amine, or combination thereof to produce a stable,
on-demand rapidly curing epoxy compound. When uncatalyzed, the
resin has an effectively infinite pot life. However, the release of
a primary or secondary amine catalyst from an encapsulated state
(e.g. in a shell, or capsule, etc.) dispersed throughout the
adhesive resin system mixture provides a dramatically accelerated
cure. Exemplary acrylate resins include monoacrylates, diacrylates,
triacrylates, tetraacrylates, pentaacrylates and combinations
thereof. Contemplated thiol curing agents include pentaerythritol
tetrakis(3-mercaptopropionate); trimethylolpropane
tris(3-mercaptopropionate); 1,3,4-thiadiazole-2,5-dithiol;
poly(ethylene) glycol dithiol; toluene dithiol; benzene dithiol;
1,2-ethanedithiol (and increasing MW alkane dithiol);
tris[2-(3-mercaptopropionyloxy)ethyl] isocyanurate (and other
polyols grafted onto isocyanurate backbones), and combinations
thereof, etc. Contemplated primary and secondary amines to be
encapsulated include, particularly, aliphatic primary amines and
aliphatic secondary amines. This system is outlined in the block
diagram shown as FIG. 4. According to system 40, acrylate
resin-based compound 42 is mixed with a thiol 44 and an
encapsulated primary or secondary amine catalyst 46. It is
understood that the specific order of mixing the three components,
may occur in any order. That is, the thiol 44 may be mixed with the
acrylate resin-based catalyst 42, or the acrylate resin-based
compound 42 and the primary or secondary amine encapsulated
catalyst 46 may be mixed first, with the thiol 44 then added. The
mixture is then exposed to an ultrasonic source 47, which causes
the encapsulated primary or secondary amine catalyst 46 to rupture,
causing the curing 48 of the adhesive mixture.
According to yet another contemplated system, an epoxy resin is
combined with an encapsulated trifluoro amine compound to produce a
stable, on-demand rapidly curing epoxy compound. When uncatalyzed,
the resin has an effectively infinite pot life. However, the
release of a trifluoro amine compound catalyst from an encapsulated
state (e.g. in a shell, or capsule, etc.) dispersed throughout the
adhesive resin system mixture provides a dramatically accelerated
cure. Exemplary epoxy resins include digylcidyl ethers of bisphenol
A; dicgycidyl ethers of bisphenol F;
N,N,N',N'-tetragylcidyl-4,4'-diaminophenylmethane; p-amino phenol
triglycidyl ether; epoxy phenol novolac resins; epoxy cresol
novolac resins; 1,3,5-triglycidyl isocyanurate;
tris(2,3-epoxypropyl)isocyanurate (and isocyanurates); glycerol
diglycidyl ether; trimethylolpropane triglycidyl ether, and
combinations thereof, etc. Contemplated encapsulated trifluoro
amine compounds include boron trichloride methyl amine, boron
trichloride ethylamine, and homologues, boron trifluoride methyl
amine, boron trifluoride ethylamine and homologues, boron
trifluoride dimethylamine, boron trifluoride diethylamine, and
homologues, boron trifluoride trimethylamine, boron trifluoride
triethylamine, and homologues, boron trifluoride piperadine, boron
trifluoride hexylamine, and combinations thereof.
This system is outlined in the block diagram shown as FIG. 5.
According to system 50, epoxy resin-based compound 52 is mixed with
an encapsulated tri-fluoro amine complex catalyst 54. The mixture
is then exposed to an ultrasonic source 56, which causes the
encapsulated catalyst 54 to rupture, causing the curing 58 of the
adhesive mixture.
Methods of encapsulating accelerator species include those methods
known to those skilled in the field of polymer-based encapsulation.
Such encapsulation methods include layer-by-layer complex
coacervation; double emulsion techniques; interfacial
polymerization; silica-shell microencapsulation; nanoparticle
embedded microencapsulation, etc.
Layer-by-layer complex coacervation involves the emulsification of
catalyst droplets (typically tertiary amines) in an aqueous
solution stabilized by a charged surfactant. An oppositely charged
high molecular weight polyelectrolyte is then introduced into the
aqueous phase to complex with the surfactant charge.
Polyelectrolytes of alternating charge can then be added
sequentially to increase capsule wall thickness and robustness.
In double emulsion techniques, an aqueous amine-loaded solution is
introduced into organic solvent containing dissolved polymer with
surfactant, and produces a water-in-oil emulsion, followed by slow
addition of this solution into a larger aqueous mixture-containing
surfactant. The organic phase is slowly evaporated with stirring to
condense out the rigid polymer shell.
Interfacial polymerization involves a catalyst to be encapsulated
being dispersed in a continuous phase with a component added to
react with the catalyst at the interface. Formation of the capsule
or shell wall is promoted by reacting functional groups that can be
catalyzed or uncatalyzed. The thickness of the capsule layer (i.e.
the shell wall) is limited by the diffusion of reactive species as
the layer is polymerized.
Silica shell microencapsulation involves a hydrophobic catalyst
being emulsified with surfactants containing hydroxyl groups in a
continuous phase of basic water. Tetraethyl orthosilicate, or
similar silyl ether capable of condensation reactions, is
hydrolyzed and added drop-wise to a stirring solution of emulsified
catalyst forming a silica shell around the emulsion.
Nanoparticle embedded microencapsulation is a technique involving
the emulsification of catalyst droplets (typically tertiary amines)
in an aqueous solution stabilized by a charged surfactant. An
oppositely charged high molecular weight polyelectrolyte is then
introduced into the aqueous phase to complex with the surfactant
charge. Polyelectrolytes of alternating charge can then be added
sequentially to increase capsule wall thickness and robustness. The
nanoparticles can be substituted in for a polyelectrolyte layer,
thus embedding the particles in the shell of the microparticle.
Ultrasonic sources for rupture of capsules can involve a range of
frequencies from about 20 kHz to about 50 MHz. According to aspects
of the present disclosure, it is particularly advantageous to
target frequencies corresponding to the natural frequencies of a
hollow shell so as to best promote resonance and capsule
disruption. The predictive equation for natural frequency of a
shell is determined by shell dimensions such as radius and wall
thickness along with the shell material properties such as
Poisson's ratio, Young's modulus and density. For capsules in the
range of from about 10 to about 100 .mu.m with shell wall thickness
that is 1-10% of the radius, the natural frequency of a shell
corresponds to frequencies from between about 0.5 to about 10
MHz.
.alpha..times..pi..times..times..times..rho. ##EQU00001##
.alpha..times..times..times. ##EQU00001.2## R=Radius et shell
midpoint h=Shell thickness .rho.=shell density .nu.=Poisson ratio
E=Young's Modulus
Known ultrasound sources range from frequencies between about 20
kHz and about 50 MHz. Probe tip instruments capable of submersion
in a liquid, and that can disperse acoustic energy isotropically,
are known to perform in a low frequency range of from about 20 kHz
to about 100 kHz. Such isotropic sources direct large fractions of
generated energy into areas that are not of interest to the aspects
of the present disclosure. Due to the particular geometry
requirements concerning aspects of the present disclosure relating
to liquid shims for metal and CFRP-containing components, it has
been discovered that an efficient ultrasound dispersing system
would take the form of a probe that is placed into direct contact,
or substantially direct contact with an aluminum or CFRP component
panel. In this way, the ultrasonic generated acoustic energy is
focused onto a concentrated area that is set substantially at the
distance where the shim material resides. Aspects of the present
disclosure contemplate modifying focused ultrasound technology and
sources manufactured from curved piezoelectric ceramic heads
capable of being assembled into handheld-sized probes tuned to
frequency ranges between from about 0.5 to about 50 MHz. Such a
system would be advantageous, both because of the high level of
acoustic energy and pressure (about 1 MPa), and the frequency of
the applied energy residing near the natural frequency of the
catalyst particles (from about 1 to about 10 MHz for a particle
size of from about 10 to about 100 .mu.m).
FIGS. 6 and 7 show a diagram of a focused high intensity ultrasound
probe placed in direct contact with an aluminum (Al) or a carbon
fiber reinforced plastic (CFRP) panel of a component. As shown in
FIG. 6, an ultrasound triggering system 60 comprises an ultrasound
(US) source probe 62 located proximate to and in contact with the
exterior surface 66 of a first component 64 having a first interior
surface 64a. A second component 65 has an interior surface 65a. As
mentioned, the components 64, 65 may be made from a solid or opaque
material such as, for example, aluminum or carbon fiber reinforced
plastic (CFRP). The components 64, 65 are located a distance apart,
creating a gap 67 between components 64, 65. The gap 67 is
understood to be less than about 3 mm. A liquid shim material 68 is
disposed as a sandwiched layer between interior surfaces 64a and
65a of components 64, 65. The geometry of the head of the
ultrasound probe 62 is able to take into account the thickness of
the component wall and location of a liquid shim material layer 68
to deposit the highest acoustic energy density within the shim
material layer to give the greatest potential for capsule rupture
and successful cure trigger.
FIG. 7 shows an experimental setup for a system 70 where a 1 mm
layer of a non-cured epoxy-resin containing adhesive layer 72
deposited on an interior surface 76 of a carbon fiber reinforced
plastic (CFRP) panel 74. The adhesive layer comprised an
encapsulated catalyst. An ultrasonic transducer 78 is placed on the
exterior surface 77 of CFRP panel 74. Upon activation of the
ultrasound transducer 78 (at an energy of 1 MHz over a curing
duration of 60 seconds), the adhesive layer was cured. As shown in
FIG. 7, the CFRP panel 74 has an adhesive 72 provided to
demonstrate an "open-face" aspect, for curing an adhesive layer
through applying an ultrasound energy source to rupture
encapsulated catalyst present in the adhesive mix. Such "open-face"
systems may occur in manufacturing, for example, when materials,
such as, composite materials require the presence of an adhesive
material to bond with the composite and "build up" an area of the
composite material. Such open-face systems will benefit from
aspects of the present disclosure. In such uses, the adhesive
systems are applied to one surface of a material, but then can be
cured by applying an ultrasound source that can be focused to a
region or point located within the adhesive layer, for a
predetermined time and at a predetermined intensity to insure the
desire curing of the adhesive system. It is understood that if the
adhesive is applied, for example, to the interior surface of a
component, the ultrasound source may be located proximate to the
exterior surface of the component, or vice versa. While aspects of
the present disclosure contemplate curing an adhesive "through" a
solid structure, aspects of the present disclosure also contemplate
positioning an ultrasound source proximate to, but not necessarily
in contact with, the adhesive layer itself.
Examples for Catalyst Encapsulation
Layer-by-Layer--Complex Coacervate
Oil in water emulsions were prepared by processing 98 g of NaOH
(0.01 M) and 2 g of dimethyltetradecylamine (DMTDA) and 0.02 g of
cetyltrimethylammonium bromide (CTAB) by two runs through a
microfluidizer. The formed emulsion was stirred at high speed via
stir bar for 45 minutes, while 200 mg of poly(styrene sulfonate)
(PSS) in 50 mL of water was added drop-wise to the emulsion via
syringe pump. Formation of capsules was confirmed via optical
microscope.
Double Emulsion Solvent Evaporation
Poly(caprolactone) shell material (1 g) was dissolved in 40 mL of
dichloromethane. An internal water phrase was prepared by combining
1.5 g of NaOH (0.01 M) solution with 0.03 g sodium
dodecylbenzenesulfonate (SDBS), and 1.5 g of triethylenetetramine.
The internal water phrase was added to the oil phase and the
resulting mixture was agitated via a dispersion disk at 1900 rpm
for 15 minutes. The first emulsion was then added to 250 mL of a
0.16 wt. % solution of SDBS in water, which was agitated by stir
bar. The solution was maintained at 40-45.degree. C., for
approximately 6 hours until the dichloromethane had evaporated
leaving hard poly(caprolactone) shells. Formation of capsules was
confirmed via optical microscope. Subsequent experiments varied
amounts of poly(caprolactone) in order to create shell walls of
varying thickness.
Interfacial Polymerization
An internal oil phase composed of 20 g dimethyl para-toluidine
(DMPT), 15.94 g pentaerythritol tetrakis (3-mercapto-propionate)
(PTMP), and 11.85 g trimethylolpropane triacrylate (TMPTA) were
mixed and suspended in 500 mL 1.28 wt. % poly (vinyl alcohol) in
deionized water via dispersion disk at 2100 rpm for 30 minutes. The
dispersion disk rate was then decreased to 1700 rpm, 0.9 mL
octylamine was added, and agitation was allowed to continue for one
hour. Formation of capsules was confirmed via optical
microscope.
Silica-Shell Microcapsule Preparation
In a beaker, Pluronic P123 (0.08 g) was dispersed in water
containing NaOH (0.1 M NaOH, 50 mL). The solution was heated to
35.degree. C. under constant stirring until Pluronic P123 was fully
dissolved. Next, N,N-dimethyl tetradecylamine (5 g, 20 millimole)
was added to the solution and continuously stirred for 3 hours to
form stable emulsions. In a separate beaker, tetraethyl
orthosilicate (TEOS, 5 g 24 millimole) was added to an HCl aqueous
solution (pH 2.45) and stirred at 35.degree. C. until a homogenous
solution was obtained. The contents from this beaker were then
added to the emulsion solution drop-wise, and allowed to stir for
24 hours to complete microcapsule assembly. The white precipitate
at the surface of the solution was collected, rinsed and allowed to
dry. N,N-dimethyltetradecylamine having a lower density than water
is expected to be at the surface after encapsulation.
Capsule Rupturing
Capsules prepared according to each outlined method above, were
suspended in a variety of low viscosity solvents (methanol,
acetone, and water) and subjected to low frequency ultrasonic
waves. Capsule rupturing was monitored by colorimetry (ninhydrin
test), pH analysis, and optical microscopy. Further, capsules
prepared by solvent evaporation and interfacial polymerization were
isolated, incorporated into an epoxy/thiol resin, and disturbed by
both ultrasonic waves and pressure.
Focused Ultrasonic Curing
Aluminum-filled adhesive paste was prepared by combining 1.25 g of
a 3:1 mixture of Araldite MY 721 to Araldite EPN 9850, 1.25 g PTMP,
2.5 g aluminum powder (Toyal 5621) and 0.25 g DMTDA (amount
adjusted for encapsulated DMTDA using 1% w/w) and mixing via
centrifugal mixer. The paste was applied in about 1/8'' thick strip
on an aluminum substrate and tested for Shore D hardness as the
cure proceeded. A 1 MHz focused ultrasound probe (Precision
Acoustics, Dorchester UK) was applied to the back side of a carbon
fiber reinforced plastic (CFRP) panel (1.52 mm thick) using a
custom made polymeric lens between the probe head and CFRP
backside. Acoustic gel was applied to eliminate air gaps between
the probe head and sample. The probe head was submerged in a water
bath with the CFRP panel exposed on the surface and a 1 MHz
sinusoidal voltage signal (80V peak to peak) applied for 60
secs.
The preferred variations and alternatives of the present disclosure
relate to the manufacture and use of components and parts of any
dimension having gaps for which the use of a liquid shim would be
required or desirable, including the manufacture and use of
components and parts in the fabrication of larger parts and
structures. Such devices include, but are not limited to,
components and parts designed to be positioned on the exterior or
interior of atmospheric and aerospace vehicles and other objects,
and structures designed for use in space or other upper-atmosphere
environments, such as, for example manned or unmanned vehicles and
objects. Contemplated objects include, but are not limited to
vehicles, such as, for example, aircraft, spacecraft, satellites,
rockets, missiles, etc. and therefore include manned and unmanned
aircraft, spacecraft, terrestrial, non-terrestrial, and even
surface and sub-surface water-borne vehicles and objects.
FIG. 8 is a drawing of an aircraft 80 with a section 82 enlarged
and showing a fuselage panel 84 comprising components having liquid
shims (not shown) present in component parts used to construct
fuselage panel 84.
When introducing elements of the present disclosure or exemplary
aspects or embodiment(s) thereof, the articles "a," "an," "the" and
"said" are intended to mean that there are one or more of the
elements. The terms "comprising," "including" and "having" are
intended to be inclusive and mean that there may be additional
elements other than the listed elements. Although this disclosure
has been described with respect to specific embodiments, the
details of these embodiments are not to be construed as
limitations. While the preferred variations and alternatives of the
present disclosure have been illustrated and described, it will be
appreciated that various changes and substitutions can be made
therein without departing from the spirit and scope of the
disclosure.
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